Exodus 17:11-12

11When Moses lifted up his hands, the Israelites were winning in the fight. But when Moses brought his hands down, the Amalekites were winning.

12Moses' hands became very tired. So Aaron and Hur put a big stone under Moses for him to sit on. Then Aaron and Hur held up Moses' hands. Aaron stood on one side of Moses, and Hur stood on the other side. They held his hands up, until sunset.